Blast Off! (9 page)

Try It Yourself: Bottle Rocket Blastoff

Rockets work by pushing exhaust downward (really fast), which pushes the rocket upward (really fast). You can build your own bottle rocket that uses air pressure to push water downward out of the rocket, which will propel the rocket upward for a big launch.

 

Y
OU WILL NEED
:
2-liter soda bottle, cardboard, duct tape, a bicycle pump with a pressure gauge, an inflation needle, a rubber stopper, and some stakes.

 

Building Your Rocket

1. Make sure the rubber stopper can be inserted into the end of the soda bottle so it holds air inside. You can check for a seal by squeezing the bottle when the stopper is pushed in.

2. With the help of an adult, drill a small hole through the stopper so that when you push the inflation needle in, it fits tightly. Try starting with a smaller drill bit than you think you'll need, and redrill the hole bigger later if you really need to. The goal is to have the rubber tight around the needle, making a good seal.

3. Push the inflation needle through the rubber stopper till the end pokes out a little bit. The end with the small hole should be poking out of the smaller tapered end of the stopper.

4. Add fins and a nose cone to your bottle to turn it into a rocket! You can design them however you want. Putting the fins near the rocket's nozzle will help it go straight.

5. Build a launchpad by driving some stakes or sticks into the ground so that your rocket can sit upright while you're pumping the air in.

6. Attach the bike pump's nozzle to the inflation needle that's now going through the stopper. Now we're ready to fly!

Launch Sequence

1. When you don't know how something works yet, it's always safer to start small. Do an air test by gently pushing the stopper into the nozzle. Put the rocket on the launchpad and pump air into the bottle till the stopper pops out. Try to watch the pressure gauge on the bike pump and see what pressure made the stopper pop out.

2. Do a second air test by pushing the stopper into the rocket nozzle with a little bit more force than last time. Put the rocket back on the pad and pump again till the stopper pops out. You may see a little launch this time, and it should have taken more pressure than last time to force the stopper out. Cool! All systems are “go” for launch.

3. Put some water in the bottle, push the stopper back in, stand back, and start pumping! This time, the rocket should get at least a little launch if the pressure was around 10 PSI or higher before the stopper popped out. Now your rocket works; it's time to do some experiments!

 

Experiment Time

1. Try varying the amount of force you use to insert the stopper each time. What happens when you push it in very lightly versus with more force? How does it change the pressure required for a launch?

2. Change the amount of water you put in the rocket for each launch. What other important property of the rocket changes when you add lots of water versus a little bit?

3. Test out some different nose cones. Does the rocket fly better with a big, long nose cone that's heavy? How about a short one that uses less material?

4. Vary the size and placement of the fins. What would you need to do to make the rocket spin on its way up?

 

Tips

•   When you're trying to learn about something by changing things, it's important to only change one thing at a time so you can see what a difference it made. That means if you're trying out different nose cones, try to use the same amount of water and air pressure for each launch. That way, if the rocket's flight changes from trial to trial, you know it's because of the different nose cone and not something else.

•   If you think you have an idea that explains how something works, think of ways to test out if that idea is true! Do you think that the air pressure is related to how high the rocket flies? How would you test that out?

•   Be patient with yourself! When you're trying something new, it might not work right the first or second or third time you try it. Maybe even more times than that. Learn by making observations about the rocket's performance so you can make the right adjustments as you proceed.

 

Safety Notes

•   Rockets store and release a lot of energy! Always make sure that if the rocket were to launch when you don't expect it to, it won't hit anything or anybody that's nearby.

•   Make sure everybody around knows that you're going to launch when you're pumping air into the rocket. Doing a countdown helps, especially if you know how many pumps it takes to launch your rocket.

•   If you've pumped a lot of air into the rocket and the pressure is high but the rocket's not launching, don't go up to the rocket and try to pull the stopper out. It might launch before you're ready and hit you! Instead, wait till the pressure dies down and reinsert the stopper with less force than you used last time.

Excerpt from
Alien in My Pocket: The Science Unfair

A
mp sat on the alarm clock I kept next to my bed. My mom was waiting downstairs to drive me to school. The time on the clock told me I had missed the bus fifteen minutes ago and would probably be late for school. I also hadn't finished my homework, and I didn't have an experiment for the science fair yet. So really, being late was the least of my worries.

“Listen, Amp, I have a D in science right now,” I said with as much patience as I could muster. “Miss Martin told us—”

“What's the D stand for?” he interrupted.

“It stands for . . . ,” I began, trying to remember what the D stood for. “I can't remember! The D stands for disaster, okay! Or dummy! Or dimwit! It doesn't matter what it stand for. It's bad!”

“If it stands for bad, it should be a B, not a D,” he said.

“No, a B is good,” I said.

“Good should be a G then, right?”

“Gosh dang it, Amp!” I howled. “You can't change the grading system that's been around since my parents were kids. You're missing the main point.”

“Hey, I have a great idea for a science experiment.”

“Oh, yeah?” I said nervously. A great science fair experiment would definitely help my grade. “What?”

“I'd need some special equipment, of course, and I'd need to sequence a sample of your DNA, but growing a third arm would be really interesting, and easier than you think.”

I stared at him. He was either clueless or intentionally trying to make me angry. I could never tell which. “I can't grow another arm!” I shouted. “None of my shirts would fit.”

“But you'd be a heck of a juggler,” he said softly.

“I can put you in a hamster cage, you know,” I said.

“Okay,” he said, holding up both hands in surrender. “I'm just asking that you think about it.”

I grabbed my head and squeezed it, which, surprisingly, helped me remember something. I jumped up and pulled my science textbook out of my backpack and flipped through the pages. There were twenty or so suggestions for classroom experiments in the glossary in the back. One caught my eye. It showed a potato with a bunch of wires stuck in it and a small lightbulb that was lit up next to it. It was labeled
POTATO BATTERY
. All I'd need was a potato, some wires, and a lightbulb. How hard could that be?

“Easy,” I announced. “I'm going to make a battery out of a potato.”

I dropped the book on my bed and pointed to the two photos.

Amp leaped onto the bed and stepped onto the open page. He read in silence. Studied the photos for a minute, stroking his tiny blue chin the whole time.

“Seems kind of dull,” he said.

“No, it seems easy. A simple potato battery is perfect.”

“Whoa, someone didn't brush his teeth this morning,” Amp said, waving his hand in front of his face.

“Funny,” I said. “That's what I'm making.”

“Fine, but I should warn you that—”

Just then my door popped open and my mom stuck her head in.

I whipped my head in Amp's direction.

But Amp was gone. I looked around, but, thankfully, he had vanished. Mom hadn't noticed. He really was the fastest thing I had ever seen—or not seen.

“Who on earth are you talking to up here?”

“I'm . . . . I'm practicing my science fair presentation,” I said weakly.

“You're still doing your homework, Zack?” She sighed. “C'mon, I need to get to work. Better fix that hair first, honey.” She headed back down the hallway.

“One second, Mom,” I called after her.

“Between her popping in all the time and your brother snooping around, I'm getting nervous about being discovered.”

I froze. “What? Taylor's been in here? Looking around? Has he seen you?”

“No, because I usually make myself invisible. Would you like me to tell you how?”

“No, I don't care how. We just can't get caught. If someone sees you they'll take you away, Amp. Then you'll never get home.”

Amp looked concerned. “One of these days our luck will run out, Zack. I think your brother is suspicious. We need to get my spaceship repaired!”

“We will, Amp. As soon as I get through this science fair. I can only handle one disaster at a time.”